Mortgage Amortization Calculator

Each row represents one month and shows: payment, interest portion (running balance × monthly rate), principal portion (payment − interest), and the new running balance. Sum the principal column across all months and you get back to the original loan amount; sum the interest column and you get the lifetime interest cost.

The pattern: month one is mostly interest. Month 360 is mostly principal. The crossover (where principal exceeds interest in a single payment) typically lands around year 17–22 of a 30-year loan, depending on the rate. Until that crossover, every regular payment is paying more for the privilege of borrowing than to actually retire the debt.

An extra principal payment in any given month immediately reduces the balance that all future interest is calculated on. The schedule recomputes from that point forward — earlier payoff, lower total interest, and a faster crossover where each payment is mostly principal.

$100/month extra principal on a $300,000, 30-year, 7% loan: ~3.5 years saved, ~$45,000 in interest. $300/month extra: ~9 years saved, ~$130,000 saved. The relationship isn't linear — additional principal has progressively less leverage as the loan shortens, but in the early years even small extras compound for decades.

Equity is the home's value minus what you owe. The amortization schedule shows the loan-side of equity directly: home value minus the running balance equals the equity contributed by paydown (separate from market appreciation).

The 80% loan-to-value threshold matters for two reasons: PMI cancellation on conventional loans (the lender drops PMI automatically at 78% LTV, by request at 80%), and the eligibility for a HELOC or home equity loan (typically 80–90% combined LTV cap). The amortization schedule shows when you cross 80%; for a 20%-down loan, this is typically year 8–10 on a 30-year at 7%, sooner with extra principal.

Itemizers can deduct mortgage interest on up to $750,000 of acquisition debt (post-TCJA). Because the early-year interest is so high, the deduction is largest in the first years of the loan and shrinks over time. A $300,000 mortgage at 7% yields ~$20,800 of interest in year one and ~$2,500 in year 30.

Most filers post-TCJA take the standard deduction (~$14,600 single, ~$29,200 MFJ for 2024) and don't itemize. The mortgage-interest deduction often only matters in early years when interest is high and possibly only for high-state-tax filers whose total itemizable deductions exceed the standard deduction. The amortization schedule shows whether your mortgage interest in a given year is large enough to make itemizing worthwhile.